A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to an analog or digital code. There are two main types of rotary encoders, i.e., absolute and incremental (relative). An incremental rotary encoder provides cyclical outputs when the encoder is rotated. Incremental rotary encoders may be either mechanical or optical. The mechanical type is typically used as a digital potentiometer on equipment including consumer devices. For example, most modern home and car stereos use mechanical rotary encoders for volume control. The incremental rotary encoder is the most widely used of all rotary encoders due to its low cost and ability to provide signals that can be easily interpreted to provide motion related information such as position, velocity and RPM. More information regarding incremental rotary encoders may be found, for example, on the Internet at Wikipedia.